1. Field of the Invention
The present invention relates to an image forming apparatus for forming images on recording media.
Examples of image forming apparatuses include an electrophotographic copying machine, a laser beam printer, a work processor, a facsimile equipment and the like.
2. Description of the Related Art
A color image forming apparatus is described below as an example of image forming apparatuses.
Conventional color image forming apparatuses frequently employ an electrophotographic system using multiple transfer, as shown in FIG. 21. In this example, an image holding member 3 serving as an electrophotographic photosensitive drum is supported so as to be rotatable in the direction of an arrow. The photosensitive drum 3 is uniformly charged by charge means H and then irradiated with light by a laser exposure device L to form an electrostatic latent image on the photosensitive drum 3. The latent image is changed to a visible image, i.e, a toner image, by a development device 1 which contains color developers of, for example, yellow (Y), magenta (M), cyan (C), black (BK) and the like.
On the other hand, a transfer material 7 is conveyed so as to be fixed to the surface of a transfer device 2, for example, in a drum-like form, by electrostatic adsorption or means such as a gripper or the like. The color image on the photosensitive drum 3 is transferred to the transfer material 7 wound on the transfer device 2, i.e., a transfer drum in this example.
This example is further described below. The electrostatic latent image formed on the photosensitive drum 3 by exposure based on a image signal of a first color is first visualized by a development unit 1a containing, for example, a yellow (Y) developer, and then transferred to the transfer material 7 held on the transfer drum 2. After the developer remaining on the photosensitive drum 3 is cleaned off by a cleaner 4, an electrostatic latent image of a second color is formed on the photosensitive drum 3 by exposure based on an image signal of the second color and is visualized by a development unit 1b containing, for example, a magenta (M) developer. The resultant visual image is then overlapped on the first visible image of yellow transferred to the transfer material 7 on the transfer drum 2 and transferred thereto. Toner images of third and fourth colors, for example, cyan (C) and black (BK), respectively, are then overlapped and transferred to the transfer material 7 on the transfer drum 2 by repeating the above-described process. The transfer material 7 is then separated from the transfer drum 2 by a separation device 6, and the color images are fixed by a fixing device 5 to obtain a permanent image.
In the above-described color image forming apparatus using a multiple transfer process, defective feeding of the transfer material 7, i.e., a jam, frequently occurs in holding area a where the transfer material 7 is held by the transfer drum 2 and separation area b where the transfer material 7 is separated from the transfer drum 2, both areas being shown as shadowed portions in FIG. 21.
When the leading end of the transfer material 7 separated from the transfer drum 2 in the separation area b has already been conveyed to the fixing device 5, there is sometimes the danger of producing a complicated jam, i.e., a jam of the transfer material 7 over the range from the fixing device 5 and the transfer drum 2.
In conventional apparatuses, when such a jam occurs, one side (the side shown in the drawing) of the apparatus body is opened, the transmission of driving to the transfer drum 2 is manually released, and the transfer material 7 causing defective conveyance is pulled out to the side of the body while the transfer drum 2 is manually rotated.
However, in the above-described method of dealing with a jam in the conventional apparatuses, since the transfer drum 2 and the photosensitive drum 3 must be manually rotated for puling out the transfer material 7 wound on the transfer drum 2, the work is troublesome. Further, since the jammed transfer material 7 is removed in the direction perpendicular to the direction of conveyance of the transfer material 7, there is produced the problem that the surface of the transfer drum 2 is rubbed with the transfer material 7 and damaged thereby.